DIY Electric Car Forums banner

Locost EV conversion log

10143 Views 86 Replies 11 Participants Last post by  Wayne Alexander
Hi everyone,

I am still in the early planning stages here, but I thought I may as well start a thread to document some of what I'm working on/planning, both for information and feedback.

The car:
-Lotus 7 replica (AKA 'Locost'), built by myself to original book dimensions.
-Currently powered by a 2004 Yamaha R1 motorcycle engine.
-Current weight is about 1200 lbs without driver and half a tank of gas
-Primary use is Autocross, though it is street legal

-Safe and well-built EV conversion
-Torque at low speeds but still possible to cruise on the freeway
-Keep reasonably close to the same weight
-Range isn't a huge concern but 30 miles or so would be nice
-Keep costs under $10k CAD?

Here's a photo from last season:

Tire Wheel Vehicle Car Sky

So the car is obviously a front engine RWD layout (I guess, technically the engine is 'mid' since no part of it is forward of the front axle). The rear axle is a narrowed Ford 7.5" out of a Ranger. From what I can tell, it looks like I can get up to a 4.56 gearset for it. It is currently geared to 3.45, which means the engine is running at 6-7000 rpm on the highway (not good) and still doesn't have as much low end torque as I would like. Also, due to the open intake and limited space for a muffler, I am constantly within a decibel or so of going over the noise limit when I get near redline at WOT. The car will do over 60 MPH in first gear, so I rarely even hit second on the courses we typically run here.

Since I will be left without a transmission after the bike engine is out, and to keep weight down, I am planning to go directly from motor to axle with a two-piece driveshaft. I thought long and hard about a DC motor, but decided against it due to a few reasons, including choice of controllers and availability of suitable motors locally.

So I am looking at either a Leaf motor or a Hyper 9. It would be nice to use a Leaf motor for the lower cost, and bonus if I can get the charger to work with whatever batteries I choose. Right now I can't seem to find much info on using the charger, and even less info on using it with a different battery voltage.

And speaking of batteries, I'm leaning towards second gen Chevy Volt. It looks like I could fit four modules in the car - two under the hood and two in the back where the gas tank is now. The Volt battery comes with three 16s modules and four 12s modules, so I can think of two possibilities:
1. Use two of each module size to get 28s2p (actually 4p since each module is internally 2p) (Good for Hyper 9)
2. Use all three 16s modules plus one 12s in series for 60s (Leaf motor would need at least this much voltage)

Since I designed all the suspension and everything except for the basic layout of the 'book chassis', I already had a CAD model to start with. Here's what it looks like with the Hyper 9 and a Spicer PTO u-joint adapter:
Wheel Tire Vehicle Automotive parking light Motor vehicle

And finally, some of my comparisons. I had to go and wrap my head around how synchronous motors work, so hopefully this is right. I would really appreciate some feedback on this! To get the Leaf numbers, I first took the commonly available graph for the 80kW motor and scaled it up to 110kW at the same RPM. I then scaled the RPM for a given torque value, based on going from 360v to 240v.
Sky Rectangle Astronomical object Slope Parallel

If I did that all correct, it looks like the Leaf motor would give me better torque up to about 40 mph and then the Hyper 9 takes over. The MPH line assumes 4.56 gears. On one hand, I like the added low end power, but on the other hand, power is only useful if you can put it to the ground. Maybe as a next step, I should make another graph that compares wheel torque instead of driveshaft torque, and play around with different combinations of motors and rear end gears.

And that's about where I am at now. Any input is appreciated. My timeline for buying parts is basically most of the summer, then once this season is over I plan to tear the car down and start the conversion as a winter project.

See less See more
1 - 20 of 87 Posts
Floyd, actually I meant the onboard charger (and whatever controls it). I'm not actually sure at this point where the charger gets its control from. If it's onboard programming or if it just gets CAN messages (which I suspect is the case). I don't need anything fancy though, that's for sure.

Remy, well the tire force graph would look just like the torque curves if assuming infinite traction. 1345 lbs for the Leaf motor and 834 for the Hyper 9 at the peak. Not really an excel wizard but what I came up with is this:

  • They both have flat curves up to 30 mph, so assuming infinite traction, no losses etc, the 0-30 is 1.5s Leaf and 2.5s Hyper 9 (ha, yeah right!).
  • 30-60 is trickier but if I average the acceleration of the Leaf motor through speed range, I get 2.2s Leaf and 2.5s again for the H9 since it's still in constant torque.
  • Total times for both would be 3.7s for the Leaf and 5.0s for the H9.

Where it gets more interesting is 60-80. Using the same averaging of acceleration method, 7.8s for the Leaf and only 5.7s on the H9. Therefore 0-80 is 11.5s Leaf and 10.7s Hyper 9.

Thanks for the idea, that tells a very interesting story! And you're right, the H9 would be better if geared lower..
See less See more
  • Like
Reactions: 1
If it was mine I would cut the back out and put the entire Leaf unit in there -
making up a rear suspension setup would be relatively easy and it should be better than a live axle
I have a subaru rear diff with MacPherson struts - easy to make and works well
That would also give you the entire front engine bay AND the old transmission tunnel area for batteries

Your acceleration times are a bit slow - I'm doing 95 mph in just under 8 seconds
Yeah, I have been thinking about that. Will continue to keep the idea in mind, but there would also come a point where I decide to build a whole new car a few years down the road. Maybe even something with a Bolt (or Tesla?) motor...

As for the acceleration, I guess it's really coming down to motor kW and gearing.. Though I have been reading about people extracting more power out of the Leaf motors. One option might be to use 4.10 gears instead of 4.56 and plan on upping the current coming out of the inverter a bit.

What's your final drive ratio?
The math above was done assuming a direct coupling to the diff, and 4.56 gears in the diff (though see above for my second thoughts on that).

Yes, "front-mid engine"; Nissan even named one of its platforms FMR in recognition of this configuration.

The motor appears to be in roughly the stock engine location. Can it go further back, in location of a Lotus 7 or Locost (but not this motorcycle-powered) transmission? That would help with space for battery in the front.
Sadly, no. Due to the bike engine layout, I did not build much of a widening into the tunnel - partly to allow myself some more room at the pedal box. The tunnel is very narrow through the middle of the car, widening to the passenger side near the front to accommodate the offset output shaft of the engine. What you see the driveshaft connecting to at the bottom of the screen is the reverse box (necessary to make the car street legal). What I would want to do is mount the center carrier bearing of the new driveshaft to the same place as the reverse box. If it makes sense to do so, I could then offset the motor to the passenger side a couple of inches for better balance, depending on battery arrangement.

Speaking of batteries, are there any other options I should be looking at, other than the Volt? They seem pretty well favored but I'm always open to other possibilities. The brand new 1.6kWh batteries that EV West sells look amazing, but way over my budget sadly.

Automotive tire Motor vehicle Bicycle fork Rim Gas
See less See more
  • Like
Reactions: 1
Yeah, the new car path would most likely be a full body, and hopefully more aerodynamic. Not sure how much I would want to be climbing over a huge sill, so I'd probably prefer batteries down the center.

After some more thought, I'm going to go ahead with a front engine conversion for the time being, and make the new build be a future goal. For the next couple years I would prefer not to start a whole new build due to other life factors, but I can at least start designing something new, completely from the ground up.

Meantime, I phoned a nearby salvage yard and asked about both a Leaf motor and Volt battery they had. Waiting to hear back on whether they can include some of the extra wiring I asked for.
Hmm, yeah it does look like I could offset the tubes but it would be pretty extensive. The inside dimension of the tunnel is 4" now do I guess I'd have to do 2.5" per side if I wanted to keep it centered.

Unfortunately the Leaf motor looks to be a good bit wider, but on the bright side it's also shorter than the Hyper 9. I'm not planning to use all of the cells from the Volt, but it looks like I could put two 16s modules right up front, one 12s beside the motor, and one each of 16s and 12s modules in the back, for a total of 72s without having to mod the tunnel. That arrangement would leave me with about 30 pounds added behind the rear axle compared with a full tank of gas. If I really had to I could move a 12s or a 16s to the back as well, but that would be a last resort.

As far as frame mods go, I did have to offset the motor to the right, so I'll have to model up a driveshaft and see what the u-joint angles look like. Probably going to have to mod the steering rack mounts, definitely relocate the 12v battery, etc. But I think it looks promising?

Tire Wheel Automotive tire Vehicle Motor vehicle
See less See more
The trouble is the Leaf motor is a high revving low torque unit - it really wants about an 8:1 final drive

The advantage of the DC forklift motors is that they are low revving high torque units
Hmm, maybe part of my problem is that I'm not understanding how to estimate power outputs of a DC motor and/or underestimating how much current I can draw from these Volt batteries in short bursts. Looking at the Warp 9 specs they say 100 ft lbs at 500 amps, so I guess I'd be looking for peaks around 1500 amps? And to do that, would I need 3 battery modules in parallel?

I guess the other thing I should look into is how to scale these graphs. A 16s+12s module arrangement would get me like 112v so I think that would be enough, but I don't know how to calculate how much torque I would end up with at a given RPM.

This is the one I'm looking at for reference:
Font Rectangle Parallel Pattern Screenshot

All this is wrong, but I'm leaving it crossed out so people know what not to do!
Edit: Alright, I think I have my head wrapped around it now. All my reading about AC motors threw me for a bit of a loop but it looks like DC is a lot simpler. It looks like if you want more torque at a given RPM, just increase the voltage proportionately. I'm going to go play with more spreadsheets now..
See less See more
Edit: This is all wrong too, same as above, leaving it here but crossed out.

Alright, gonna need this checked please. I had to sift through a bunch of information that sometimes contradicted other posts, but I think what I figured out was that for a given rpm, if you increase the voltage by a factor of x, the amperage will also increase by x, and the torque produced at that same rpm will increase by a factor of x^2. That last bit, I am least confident in, though, since it was hard to find info about how to compare power levels at the same speed. I whipped up a spreadsheet based on that assumption and checked the power in vs power out and it did seem to follow. I also found updated motor specs from Go-EV (motors made in 2010 or newer) so I plugged it all in and whooooo doggy that paints a very different picture! If this is all correct, then I guess it looks like a no-brainer. I even changed the rear end ratio in the calcs back to the 3.45 it's currently sitting at.

Font Material property Pattern Parallel Number
See less See more
Um...not really.

Voltage is proportional to speed in a DC and Current is proportional to torque.

Back EMF cuts back max current, which is why you increase voltage.

The square law you're seeing is horsepower, not torque.
dangit just when I thought I was getting somewhere.

Ok, so torque in ft-lbs = HP x 5252 / RPM, right? So let's say we are making 100 hp at 1000 rpm, I plug that in and get 525.2 ft-lbs.

If I double the voltage and double the amps I quadrouple the horsepower? So now we are making 400 hp at 1000 rpm? Plugging that number in gets me 2100.8 ft-lbs, or quadrouple the torque. What did I miss this time? If RPM isn't constant in that squared law, how would you calculate the new expected torque at a given rpm?

Looks like what I missed was that it still follows a constant torque line while hooked up to a typical controller, and just like with an AC motor, the point at which the flat line starts to decay just gets pushed further out when you add voltage.
Ah, okay, very interesting! Thank you all for all the help by the way, it's been hugely helpful.

I think on Monday I'm going to phone around to some motor rebuilders in town and see if anyone has anything that might be promising. I know there's one place that does pretty extensive testing, so they might even be able to provide me with a graph at my actual desired voltage. That would make me feel a lot better, anyway. Seems like DC controllers are getting harder to find, but I had also been looking for 2000A options. Maybe I'll open the search to 1000A models too..
Yeah, absolutely.

I think I finally have my head wrapped around all this. For anyone else who finds this in a search, this thread really helped clear things up for me too: torque of 9" dc with 144v pack?

So basically, yes, amps will have a direct proportional effect on torque. The volts side of the equation seems to just influence the max speed at which constant torque will still be made. If I go for a 1000 amp controller and a warp 9 (or, hopefully, a forklift motor with characteristics very much like a warp 9) then I should be making constant torque pretty much right up to 60 mph on 3.45 gears. I'd have 912 lb-ft of wheel torque which sounds pretty dang good. Assuming infinite traction, no losses and all that other fun stuff, 0-60 in 4.3 seconds.

Now I need to decide how to arrange batteries for that. If I buy a complete Chevy Volt gen 2 battery it will come with 3 x 16s modules and 4 x 12s modules. A 16s with two 12s would get me to 40s (or 160v at 4v/cell), but I would only have enough cells to do 2 in parallel. I don't know if it's safe to pull 500 amps through each module, need to look into that next.
See less See more
Yeah I was just editing all that, haha. Think I got it now.

Also found out that the stock fuse in a 2018 Volt is apparently rated for 350 amps. I'm trying to verify this but it SEEMS like it can pass 200% of its rated current for a period of time. If that means Chevy thinks the cells could support that much current for short periods, I may be okay running just two in parallel. Around here our autox courses are about 60-70 seconds. Probably around 15 minutes between runs.
Okay, battery has arrived! I measured the cell voltage at 3.5v, and I think their optimal storage voltage is something like 3.85v. I have a hobby lipo charger for my airplane/drone batteries that can charge up to 6s @ 5 amps. Thinking about disconnecting the BMS and everything, then using the charger to bring the cells up to storage voltage. Any issued with doing that?

I also posted in my other thread about the Leaf transmission conversion, going to be pulling the bearings off the jackshaft as soon as I can get my hands on a suitable puller, then start CADDing up a new housing.
Wood Engineering Gas Machine Composite material
See less See more
  • Like
Reactions: 1
Admittedly, most of my experience comes from RC car/plane batteries, but with those it's always recommended that you store them at a certain voltage. Otherwise they can degrade faster.

I pulled up the 2018 Volt owners manual and it says to run the battery down to 2-3 bars SOC on the dash if the vehicle is going to be stored for between 4 weeks and a year. It looks like there are 10 bars, so I'm tempted to assume that means 20-30% soc, but so far I can't correlate that to a specific voltage.
Okay, been a bit busy with other life stuff but I have the battery all torn apart and charged up to 3.65v. Each cell took 10 Ah just to go from 3.5v to 3.65v. Wow.

I was hoping to use as many parts out of the battery module as possible, but sadly I don't think I will get much.

The current sensor is a Lem DHAB S/51. Looks like it is rated for up to 350A according to the datasheet. Unfortunately it is not listed as compatible with the Thuderstruck MCU that I'm hoping to use.

The BMS/BECM is also probably not usable to me, because it doesn't seem like anyone has managed to interface with it, or use it in a configuration with fewer cells. If anyone knows differently, please let me know!

The HV contactors are an interesting one. Panasonic AEVS760122. Not a lot of hits when I googled the number, but I did find a datasheet for the AEVS series. If this is the correct datasheet, it's rated at 60A continuous, 180A for 1 minute. A bit disappointing, I was hoping they would have been rated a little higher. It has spade connectors that are approximately 5/8" wide. I can't tell if it has an economizer but at 12v it was drawing about 0.4A, which is pretty close to the datasheet. If I do reuse these, I may have to drill holes through the spades so I can bolt an eyelet, and that sounds pretty janky. What do you guys think?
Gas Technology Auto part Electronic engineering Machine
Font Material property Screenshot Parallel Number

As for the pre-charge contactor, it is labelled AEC11012 M11. I honestly haven't really looked into these. I found a datasheet for an AECN11012 that says they are good for 5A. The same sheet says the coil current is 0.117A but I haven't verified that yet. There are actually two of these relays included, I believe the other is for charging. I do plan to re-use these.

The resistor has 50W printed on it and measured 69.0 Ohms on my Fluke. I'll re-use this too.

I've also ordered my Openinverter kit and it should be arriving any day now.
See less See more
Well, the pile is growing. What we're looking at here is a gigantic EVSE, Thunderstruck MCU, 4x Dilithium BMS satellites, Dilithium touchscreen display, current sensor, LEV200 contactor. Not shown: The Openinverter board already installed in the inverter, second contactor on my bench for testing, 30ft of 2/0, Gen 1 Volt DC-DC converter, and the charger which is coming in a separate box.
Bag Electrical wiring Gas Auto part Cable

I'm working on designing an enclosure to cover the exposed DC input connections on the inverter. Already made a protective cover for storage.
Rectangle Font Art Pet supply Auto part

I'm also working on a RC economizer for the contactors. I put 12v to one for about an hour and it drew 1.2A initially, tapering to 1A as it heated up. But I wasn't entirely comfortable with how hot it got:
Automotive lighting Amber Font Heat Gas

So I think this circuit should do the trick. I'm going to try to get fancy and print a custom PCB to hold the resistor/capacitor and a smaller relay to switch the current to the coil. I think this should work decently enough. Should draw about 5w after 200ms.
Rectangle Slope Font Parallel Symmetry

I'm also still working on the Leaf transmission modification, will post an update in that thread shortly.
See less See more
PCB design is a bit of a learning curve, but I am making progress. Here's what I'm looking at for an economizer circuit for my two main contactors:
Product Font Screenshot Audio equipment Circle

Software is called KiCad if anyone is interested, and there are some GREAT tutorials here:
See less See more
Okay, ordered the boards from Oshpark. Their pricing model is you pay by the square inch, but you get three copies. Figured I'd cut the cost in half by redoing the board for a single economizer circuit since I'm getting three anyway. Feeling pretty good about that!

Product Font Technology Circle Screenshot
See less See more
  • Like
Reactions: 1
Ah, good catch. I was playing around with the circuit and decided I wasn't comfortable going as low as 5w, so I dropped R1 down to 10 ohm. I'll be testing it once the components show up, and I was careful to select components that could be easily changed if I see something I don't like.
Okay, time for another update. I've been trying to push multiple fronts simultaneously so I can hop from one task to another when I get stuck or tired of working on any one thing.

The economizer board I designed seems to work great. Apparently I picked the wrong footprint for the resistor, but thankfully it wasn't off by much and I was able to make it work by bending the leads a bit. The contactors stay nice and cool now!
Circuit component Electronic device Machine Gas Electric blue

I've been revisiting the placement of the motor and in light of the projected cost of building a custom reducer box, plus having another driveshaft made, I thought I should try harder to see if I could fit the motor in the back with an IRS setup. It's taken quite a few iterations but I think it is possible. I had to go back to the textbooks I bought on suspension design and make sure the geometry would work out (both on its own right and relative to the front suspension geometry). I think I have it in a pretty good place now. The motor is offset to the passenger side a bit, which is fine because it will help offset my own weight. I still need to add some tubes for bracing and to support the coilover, but so far so good. Losing the solid axle will save me 135 lbs plus whatever the driveshaft weighs (probably 50 lbs?), while adding back the weight of the CV axles, uprights, wheel bearings and wishbones. Lower wishbones est weight is about 3 lbs, uprights would be 2.5 if made from 6061. Not sure about the other components, but certainly the difference in unsprung weight would be huge. It would also free up space in the tunnel to run the power and coolant lines, as well as maybe some electronics (dc/dc converter?).

Sky Triangle Automotive wheel system Girder bridge Metal

Rectangle Slope Line Parallel Font

For cooling, I found an electric water pump out of a Prius, which seems to be a common choice. I don't think I want to try splitting the flow between the motor/inverter and batteries, so I'm looking at connecting them in series on one big loop. The BMS will be reading battery temp directly and I think I can get motor/inverter temp through CANBUS, but I think it would also be wise to install a flow switch or something, so if the pump fails or there's a blockage I will know about it right away. I also need to figure out a way to control the electric rad fan. A simple fan switch in the coolant would be awesome, but I can't seem to find one with a suitably low 'on' temperature. Being made for ICE engines they are all 160*F or more. Even the digital adjustable controllers don't seem to adjust low enough, and the ones that do use a radiator probe that you shove into the fins, and I don't think I'm a fan of that. Any suggestions would be appreciated.

Rectangle Font Slope Parallel Diagram

I got my hands on a used GE Wattstation EVSE, my goodness this thing is huge! I thought it was interesting that the control board has an ethernet port and multiple serial ports.. Apparently they were made to be expandable so you could connect card readers and bill people for usage if you mount it in a public space. It's only rated for around 7kW but that's still way more than I need.

Circuit component Passive circuit component Hardware programmer Electrical wiring Electronic instrument

I also got my MCU talking to my laptop and the Dilithium touchscreen. It can't really do much until it's connected to a few more things, but it was still encouraging to see. I also started on an overall wiring diagram and it's getting very complicated. Lots of details to work out there.
Table Computer Personal computer Output device Peripheral

And finally, while playing with the Leaf reducer housings I 'did a stupid' and tried to reinstall the jackshaft without first removing the grounding brush. Result: broken grounding brush. Looks like a replacement from Nissan is >$125 which seems like utter insanity to me. After searching around on my own I wasn't able to find any similar brushes. Thankfully, I eventually found a local brush supplier ( I had a great conversation with the owner Dan, and he found me something that should be a direct fit. I had no idea brush selection could be so complicated, but there are apparently many different materials and characteristics, so I'm glad I was able to talk through the application with him and make sure the replacement brush would live up to its task.
Wood Font Gas Automotive lighting Tints and shades

I think that's all for now. I have decided not to race the car for the rest of the season, so as soon as I can clear space in my garage, I will be pulling the car in and removing the ICE components. Currently my side of the garage is full of the vinyl plank flooring I am using to replace the carpet on the top floor of the house, and all that has to be done before the baby comes in October. I'm about halfway done at the moment (two rooms and the stairs done, two rooms and a hallway left). Busy busy!
See less See more
  • Like
Reactions: 1
What, no Flir pic of the economizer board and contactor???? Science demands it...

Haha, fair enough. I never looked at or touched the economizer last time, but this time I noticed the resistor was way hotter than I am comfortable with. The whole system was drawing 0.65A according to the power supply, and the voltage drop across the resistor was 5.85V, meaning the resistor was dissipating about 4 watts.. That matches the math, and since the resistor is rated for 10 watts I thought nothing more of it. However, the FLIR (and my fingertips!) tells a different story... I just tried turning the voltage down on the power supply and the contactor will close with as low as 7.4 volts running through the system. I'll have to do a few back calcs (and test it without the economizer board) and then I should be able to select a higher ohm resistor that I'd still feel comfortable using.

Purple Automotive lighting Electricity Violet Slope

At least the contactor is running much cooler as expected (despite the temperature in the room being higher than it was during my first test).

Purple Blue Water Automotive lighting Electricity
See less See more
  • Like
Reactions: 1
1 - 20 of 87 Posts